Apparatus to impart a circular translatory movement to an element such as a modulator element

ABSTRACT

An improved apparatus for imparting a circular translatory movement to an element. This apparatus comprises two lateral parallel arms linked, at one of their ends, on the upper ends of a support, by means of universal joints, and at their other end on an oscillating shaft which is parallel to the support, and a cranked driving member connected to said support and directly mounted on the shaft of a synchronous motor, whereby said support is imparted with a circular translatory movement.

APPARATUS TO IMPART A CIRCULAR T RANSLATORY MOVEMENT TO AN ELEMENT SUCH AS A MODULATOR ELEMENT 555 movedbodily behind an annular mask with a circular movement of translation, in a single plane, at a constant speed. The result is that if the image of the target coincides with the centre of the mask the light beam forming the image periodically excites a photo-electric cell placed behind the modulator. On the other hand, if the image does not coincide with the centre of the mask, the cell excitation frequency is modulated about a constant value.

In this apparatus, to maintain accurate tracking, the circular movement of translation imparted to the modulator support must be very accurate and regular, that is, there must be no interruptions or displacements, and the movement must be effected at a high speed. This is achieved by utilising a synchronous motor with a belt drive to a dual eccentric system with rods and cranks activating the modulator support. However, as soon as the speed becomes significant, the belt drive and the inherent amounts of play in the mechanical components cause irregularities in speed and positioning to appear.

Also, if the circular translational movement is to be regular, it is necessary for the radii of the circles described by the two cranks to be equal, for the distance between the axes of the cranks and the distance between the axes of the rods to be equal, and for the amounts of play to be at a minimum, all these conditions being very'difficult to realise.

French Patent No. 1,579,659 also describes apparatus of this type in which the modulator support is driven by a single crank driven by a belt from the shaft of a synchronous motor. This apparatus makes use of the principle of the deformable parallelogram and enables the attainment of greater speeds than does the apparatus described in French Patent No. 1,123,327, although the speed is still limited by the belt drive. Also, it has the drawback that the side arms of the deformable parallelogram do not remain in the same plane which causes constraining movements to appear, and thus wear in their supports. 7

It is an object of the present invention to obviate or mitigate the above disadvantages.

According to the present invention, there is provided apparatus for use in the frequency modulation of an optical beam, comprising a support structure, a shaft mounted on said support structure for rotational movement about its axis, a planar member located parallel to said axis and provided with means for mounting a modulator element, a pair of lateral arms pivotally mounted on said shaft in spaced-apart relationship for movement about parallel axes and connected by universal joints to said planar member, a cranked member connected to said planar member centrally of said unive rsal joints, and a synchronous motor directly coupled to said cranked member for imparting a circular translatory movement to the planar member.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, in which FIG. I schematically illustrates apparatus according to the present invention; and

FIG. 2 is a pictorial view of one form of apparatus according to the present invention.

In the drawings the modulator (not shown) to be moved bodily is mounted in a planar member I which lies in the plane defined by the shaft 2 and the point 3 at which the cranked shaft 19 is connected to the planar member. By means of the construction the planar member moves in a circular fashion whilst remaining in a single common plane. The ends of the shaft 2 are interconnected by means of universal swivel-joints 4 and 5, to two lateral arms 6 and 7. The forward ends 8 and 9 of the arms 6,7 are linked by a spring 10 which tends to bias them towards each other. The lateral arms 6 and 7 are connected to a rear shaft 13 at their ends I l and 12, the rear shaft 13 being capable of oscillating about its own axis as the arrow 14 shows. The connection of the arms 6 and 7 and the rear shaft 13 is effected by means of two double bearings 15 and 16, allowing the arms 6 and 7 complete freedom to describe cones l7 and 18 when they are moved by the shaft 2 which follows the circular translational movement imparted to the member 1 at the point 3 by the cranked shaft I9 whose axis 20 is directly connected to the output shaft of a synchronous motor rotating as shown by the arrow 21.

As a result, when the ends of the lateral arms 6 and 7 describe the right cones l7 and 18, the member 1 does not move out of its initial plane, and so is sub- 5 jected to no constraint.

The two arms 6 and 7, of length LI and L2, which act as cranks can, for example, describe circles of any radius, or other geometric figures. When the two arms 6, 7 are joined by the shaft 2 their ends can describe, synchronously, identical figures and in particular two circles of radius R1, R2 such that Rl/R2 Ll/L2 and it is not necessary, as is the case in known devices, for the radii of the circles described by the ends of the arms 6,7 to be equal. In this case the inequality of the distances between the ends of the shaft 13 and the shaft 2 appears as the non-parallelism of the axes of the cones formed by each arm so that the cones described by the arm ends 8,9 become ellipsoids but their projec tion in the plane of the modulators remains a circle.

In FIG. 2, the components corresponding to those shown in the diagram in FIG. I are designated by the same references. Thus, the planar member I which supports the two modulators (not shown) in mountings 22 and 23 provided for this purpose, is secured at its upper part to the shaft 2 supported on the lateral arms 6 and 7. The projecting ends of the lateral arms are held by the spring I0 at a distance corresponding to the length of the shaft 2 and the other ends at II and I2 are connected to the oscillating rear shaft I3. In this FIG. 2 the device is supported by a rigid support structure comprising a platform 24, two rear brackets 25 and 26 on which the shaft 13 is secured, so that it can rotate freely, and a front bracket 27 supporting the synchronous motor 28. The output shaft 20 of said synchronous motor 28 is connected by the crank 19 to the point 3 of the member 1 and its rotation communicates a circular translational movement to the member I.

The principal advantage of the device of the invention is the passivity of the shaft 2 and its capability of adopting, without producing any constraints, the movement imparted to it by the single crank 19. There is thus a constant load for the motor 28 and thus uniform speed.

Due to the symetry of construction the device is easy to balance and both static and dynamic balance is obtained by using a compensatory weight 29 which is placed as a counterweight of the drive point 3. This balancing, which is easy to effect, enables the device to operate without any strain on its components, and thus without wear on these, and at a high speed of operation.

In addition the mechanism of the device can accommodate very wide manufacturing tolerances. Errors in the dimensions are experienced by the modulator through the relationship of the lengths of the arms 6,7 and the radius of the circles described, but these errors do not affect directly the circular translational movement, with the result that it is possible to tolerate errors to times greater than those acceptable in the prior art.

In the illustrated embodiment the planar member 1 is capable of housing two modulators, and conveniently one may be used for tracking in the cruising mode whereas the other may be used in the full power mode.

What we claim is:

1. Apparatus for use in the frequency modulation of an optical beam comprising, a support structure, a shaft mounted on said support structure for rotational movement about its axis, a planar member located parallel to said axis and provided with means for mounting a modulator element, a pair of lateral arms pivotally mounted on said shaft in spaced-apart relationship for movement about parallel axes and connected by universal joints to said planar member, a cranked member connected to said planar member centrally of said universal joints, and a synchronous motor directly coupled to said cranked member for imparting a circular translatory movement to the planar member.

2. Apparatus according to claim 1, including a spring biasing the ends of the lateral arms adjacent the universal joints toward each other.

3. Apparatus according to claim 1, wherein said cranked member is provided with a counterbalance weight.

UNITED STATES PATENT OFFICE @EFRTIMQATE OF CORRECTION Patent No. 3,746,422 Dated July 17 1973 Inventor(s JEAN-CLAUDE CHAVANY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shownbelow:

In the heading to the patent item [30] the filing date of the French application, priority of which has been claimed, should be changed from "June 6, 1971" to,

--July 6, l97l.

ffsigned and sealed this 18th day of December 1973.

, (SEAL) Attest:

EDWARD M. FLETCHER, JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents nan QML "RM 140.1 3 

1. Apparatus for use in the frequency modulation of an optical beam comprising, a support structure, a shaft mounted on said support structure for rotational movement about its axis, a planar member located parallel to said axis and provided with means for mounting a modulator element, a pair of lateral arms pivotally mounted on said shaft in spaced-apart relationship for movement about parallel axes and connected by universal joints to said planar member, a cranked member connected to said planar member centrally of said universal joints, and a synchronous motor directly coupled to said cranked member for imparting a circular translatory movement to the planar member.
 2. Apparatus according to claim 1, including a spring biasing the ends of the lateral arms adjacent the universal joints toward each other.
 3. Apparatus according to claim 1, wherein said cranked member is provided with a counterbalance weight. 